eISSN 1308-4038
International Journal of Anatomical Variations (2014) 7: 17–18
Department of Anatomy, Melaka Manipal Medical College
(Manipal Campus) Manipal University, Madhav Nagar,
Manipal, Karnataka State, INDIA.
Published online May 27th, 2014 © http://www.ijav.org
A rare case of two additional slips in the origin of sternocleidomastoid muscle, and a varied insertion of sternocleidomastoid muscle was found during our routine dissection, on right side of the neck in an elderly female cadaver. The clinical and embryological significance of the variation is discussed. This case may be important for head and neck surgeons and for plastic surgeons doing muscle graft surgeries.
© Int J Anat Var (IJAV). 2014; 7: 17–18.
Dr. Vasanthakumar
Melaka Manipal Medical College
(Manipal Campus)
International Centre for Health Sci.
Madhav Nagar, Manipal
Karnataka State, 576 104 , INDIA.
+91 820 2922519 vasanthui@gmail.com
Received January 27th, 2013; accepted September 29th, 2013 Key words [sternocleidomastoid] [clavicular head] [sternal head] [additional head] [torticollis]
The sternocleidomastoid (SCM) which is shortly called as sternomastoid extends obliquely across the side of the neck and divides the neck into anterior and posterior triangle.
The SCM occupies key position since a host of important structures of neck like great vessels and branches of cervical plexus are overlapped by the muscle [1]. It takes origin by two heads (sternal and clavicular head), separated by a triangular depression known as the lesser supraclavicular fossa. The muscle is inserted to the lateral surface of the mastoid process and lateral part of the superior nuchal line. The clavicular fibers are directed mainly to the mastoid process and the sternal fibers are more oblique and superficial, and extend to the occiput [2]. The directions of pull of the two heads are different and the muscle is cruciate and spiraled
[3]. The motor nerve supply of the SCM muscle is derived from spinal root of accessory nerve [4]. The proprioceptive fibers from the muscle are conveyed by the ventral rami of C2 and
C3 [5]. The SCM muscle is involved in majority of the head movements and also it assists in inspiration [6]. The unknown origin and insertion of SCM, may result in spasm of the muscle, which in turn leads to a flexion deformity of the neck known as wryneck or torticollis [4]. The other muscles that rotate and flex the neck also may contribute to torticollis. The SCM variability may cause complications in surgical procedures that access vital elements like spinal accessory nerve that related to it and minor supraclavicular fossa [3].
While doing a routine dissection cervical region of 55-yearold embalmed female cadaver in the department of Anatomy, a rare and unusual variation in origin and insertion of SCM was noted on the right side of head and neck region. Two additional heads were arising from the deep fascia over the anterior triangle of the neck. One of the additional heads (AH1) united with the sternal fibers (I.SH1) and few fibers from its medial aspect were reflected medially and were inserted to the mandible (angle and base). The other additional head
(AH2) united only with sternal head (I.SH1). The origin of sternal (SH) and clavicular heads (CH) and their insertion to the mastoid process and superior nuchal line were appeared as usual (Figure 1).
Several variations of SCM were reported on its origin [4].
However, on the insertion site, there are very few variations

18
Kumar and George
1Man
1SH1
SCM
1SH2
CH
AH1
AH2
SH
Figure 1.
Superficial dissection of right side of the neck region demonstrating the variation in origin and insertion of sternocleidomastoid muscle. ( SCM : sternocleidomastoid –muscle belly; CH : clavicular head of sternocleidomastoid; SH : sternal head of sternocleidomastoid; AH1 : additional head unites with sternal fibers
– 1SH1 and attached to the mandible –1Man ; AH2 : additional head joins with sternal fibers – 1SH2 ) published [7]. Sternocleidooccipital, cleidomastoid and sternomastoid muscles in the same cadaver, supernumerary cleidooccipital muscle, more or less separate from the sternocleidomastoid muscle, cleido-occipital platysma muscle and accessory head of origin from the clavicle, were reported
[1, 4–6]. But the additional head (AH1) of sternocleidomastoid from deep fascia and accessory head of insertion to the angle of mandible and posterior part base of the mandible that we reported here is not found in the literature, at the best of our search.
SCM muscle variations with regard to the additional heads were reported many times in the literature, these variations might cause severe complications [7]. Physicians/surgeons should be aware of this anatomical variation in order to understand complications that can happen. The knowledge of variations of SCM of this type is important for head and neck surgeons, maxillofacial surgeons, and the plastic surgeons. The SCM can be used in several ways during surgery. It is used along with a part of clavicle to reconstruct mandible, and its defects, as a myocutaneous flap for reconstruction of the oral floor, as a suture line to protect carotid and innominate arteries and in parotid surgeries to prevent Frey’s syndrome [5, 8, 9]. In the surgeries of the lower part of the neck, such variations may bring complications as the important neurovascular bundle is covered by the muscle. It may be also difficult to perform invasive techniques.
The present case of SCM variability discusses the possible embryological and genetic basis of its origin. The muscle fibers for the SCM and trapezius are derived from (Hox D4+) somatic mesoderm [3]. These fibers are connected to skeletal elements, only by post-otic neural crest derived connective tissue instead of the usual pattern to the mesodermal skeletal structure [6]. Hox D4+ somites do not attach directly on to skeletal region as done by the mesodermal muscle, but these myoblasts appear to be subjugated to neural crest derived muscle connective tissue [10]. This fact best suits to the current variation, where some fibers of this muscle were merged with the connective tissue surrounding the platysma muscle and not with the skeletal elements. In conclusion the knowledge of this variation may useful to avoid complication and to obtain ideal outcome surgical results.
[1] Coskun N, Yildirim FB, Ozkan O. Multiple muscular variations in the neck region -- Case study.
Folia Morphol (Warsz). 2002; 61: 317–319.
[2] Moore KL. Clinically Oriented Anatomy.
3rd Ed., Philadelphia, Williams & Wilkins. 1992;
786–987.
[3] Standring S, ed. Gray’s Anatomy: The Anatomical Basis of Clinical Practice.
40th Ed.,
London, Elsevier, Churchill Livingstone. 2008; 441.
[4] Ramesh RT, Vishnumaya G, Prakashchandra SK, Suresh R. Variation in the origin of sternocleidomastoid muscle. A case report.
Int J Morphol. 2007; 25: 621–623.
[5] Cherian SJ, Nayak S. A rare case of unilateral third head of sternocleidomastoid muscle.
Int
J Morphol. 2008; 26: 99–101.
[6] Kumar MSJ, Sundaram SM, Fenn A, Nayak SR, Krishnamurthy A. Cleido-occipital platysma muscle: a rare variant of sternocleidomastoid muscle.
Int J Anat Var (IJAV). 2009; 2: 9–10.
[7] Bergman RA, Thompson SA, Afifi AK, Saadeh FA. Compendium of Human Anatomic
Variation.
Baltimore, Urban & Schwarzenberg. 1988; 32–33.
[8] Conley J, Gullane PJ. The sternocleidomastoid muscle flap.
Head Neck Surg. 1980; 2:
308–311.
[9] Sebastian P, Cherian T, Ahamed MI, Jayakumar KL, Sivaramakrishnan P. The sternomastoid island myocutaneous flap for oral cancer reconstruction.
Arch Otolaryngol Head Neck Surg.
1994; 120: 629–632.
[10] Matsuoka T, Ahlberg PE, Kessaris N, Iannarelli P, Dennehy U, Richardson WD, McMahon AP,
Koentges G. Neural crest origins of the neck and shoulder. Nature. 2005; 436 : 347–355.